Method of transforming carbon nanotubes

ABSTRACT

A method of transforming a carbon single wall nanotube (SWNT) is provided. The method comprises exposing the SWNT to light having a power sufficient to ignite or reconstruct the SWNT such that the SWNT is ignited or reconstructed by the exposure to the light.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a Divisional of U.S. Ser. No. 10/367,971,filed on Feb. 19, 2003, which application claims benefit under 35 U.S.C.§ 119(e) of U.S. provisional application 60/358,082, filed Feb. 19,2002, both of which are incorporated herein by reference in theirentirety.

This invention was made with government support under U.S. Department ofDefense Contract No. N000140010250. The government has certain rights inthe invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to carbon nanotubes and moreparticularly to transforming carbon nanotubes using light.

Ten years after their discovery, carbon nanotubes continue to revealfascinating features. Single-walled carbon nanotubes (SWNTs) have arange of remarkable mechanical and electronic properties due to theirunique structure, as discussed in Dresselhaus, M. S., Dresselhaus, G.,Avouris, P. “Carbon nanotubes: synthesis, structure, properties, andapplications,” Springer, Berlin, New York (2001). There has been aprevious study on the elastic response (deformation) of nanotubes tovisible light, as discussed in Zhang, Y. and Iijima, S. “Elasticresponse of carbon nanotube bundles to visible light”, Phys. Rev. Lett.82, 3472-3475 (1999). In other words, the authors of this study reportthat the nanotubes elastically deformed in response to irradiation bylight and then returned to their original shape.

BRIEF SUMMARY OF THE INVENTION

A preferred aspect of the present invention provides a method oftransforming a single-walled carbon nanotubes (SWNT). The methodcomprises exposing the SWNT to light having a power sufficient to igniteor reconstruct the SWNT, such that the SWNT is ignited or reconstructedby the exposure to the light.

Another preferred aspect of the present invention provides a method ofobtaining light emission from a nanotube, comprising exposing thenanotube to a first light such that the nanotube emits a second lightdue to the exposure to the first light.

Another preferred aspect of the present invention provides a device,comprising a device shell and a plurality of single-walled carbonnanotubes (SWNTs) located in the device shell. The device is adapted toperform a function when the SWNTs are ignited or reconstructed byexposure to light having a power sufficient to ignite or reconstruct theSWNTs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are TEM images of SWNT material.

FIGS. 2A-E illustrate a sequence of frames taken from a real-time videorecording of SWNT burning phenomena after the application of aphotography flash in air.

FIGS. 3A-D are HRTEM images of a typical areas of transformed nanotubematerial obtained after exposing the SWNTs to a flash of light.

FIG. 4 is a schematic of a memory device utilizing SWNTs.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present inventors discovered that single-walled carbon nanotubes(SWNTs) can be transformed by exposing a plurality of SWNTs to lighthaving a power sufficient to ignite or reconstruct the plurality ofSWNTs. The term “reconstruct” as used herein means a permanentstructural reconstruction, where the nanotube structure is permanentlychanged to a non-nanotube structure, rather than merely elasticallydeforming the nanotubes with subsequent recovery of the nanotubestructure.

Any light having a suitable power may be used to transform the SWNTs,such as visible, infrared or ultraviolet light. Preferably, a flash oflight is used to transform the SWNTs. For example, the present inventorshave discovered that SWNTs ignite when exposed to a standardphotographic flash at a temperature below SWNT ignition temperature,such as at room temperature. However, other light sources, such ascommercial flash lamps used in materials processing and rapid thermalannealing may also be used. Also temperatures below SWNT ignitiontemperature other than room temperature may also be used if desired.

The average power required for ignition of SWNTs varies depending on theSWNT density and ambient in which the SWNTs are located. For example,the average power required for ignition of SWNTs in the presence of airis only about 100 mW/cm² (±20 mW) for a sample density of about 0.2g/cm³ for a pulse of visible light having a rise time of 50 μs and adecay time 1.2 ms. When the sample is compacted to higher densities,larger power is needed in order to ignite the SWNT material. Forexample, for SWNT densities of greater than 1 g/cm³, ignition occurs atabout 300 mW/cm².

A large photo-acoustic effect, observed in other carbon structures, isalso associated with the ignition phenomenon. The present inventorsnoted that ignition is inhibited if the SWNTs sample is densified andthat ignition is not observed at available powers for multi-wallednanotubes, graphite powder, carbon soot or C₆₀.

Surprisingly, even in the absence of ignition, SWNTs undergo totalstructural reconstruction in the presence of air, vacuum, or inertgases, upon exposure to a light flash of a sufficient power lower than apower required for ignition. The reconstruction occurred at atemperature below a temperature which SWNTs are reconstructed (i.e.,converted to amorphous carbon or other carbonaceous material). Theignition and reconstruction phenomena, witnessed after the absorption oflight, are sensitive to the competition between the high thermalconductivity along the carbon nanotube axes, which may lead to intenselocal heating, versus loss of thermal energy into the bulk, includingthe surrounding gas. The photo-induced transformation effectsdemonstrate how the SWNT materials structured on the nanometer scalegive rise to surprising properties compared to bulk materials.

When SWNTs are exposed to the suitable light flash, such as a standardcamera flash, to ignite, the ignited SWNTs burn leaving behind a smallamount of residue consisting of oxidized metal particles used for thecatalytic growth of SWNTs and carbonaceous material. The carbonaceousmaterial comprises mostly amorphous and partially graphitized carbon aswell as carbon nanohorns. After flashing the SWNTs, there is also anassociated photo-acoustic effect caused by the absorption of incidentlight on the sample and the subsequent rapid rise of heat within theSWNTs, leading to expansion and contraction of trapped gases, thusgenerating acoustic waves, see Chen, H. and Diebold, G., “Chemicalgeneration of acoustic waves: a giant photoacoustic effect.” Science270, 963-966 (1995).

The present inventors have found that this photo effect transformationoccurs for all SWNTs samples whether prepared by the electric arc, laserablation or chemical vapor deposition, when these samples are exposed toa camera flash at close range (several cm away from the sample). Allspecimens with low nanotube yield, such as samples containing nanotubefractions of about 50% and samples that are essentially pure nanotubes,for example, powder samples commercially available from the HiPCoprocess, containing nanotube volume fractions of greater than 90%,ignite in air. The photo induced transformation occurred on dry,“fluffy”, as-prepared nanotube samples, as will be described in moredetail in the specific example section below. However no ignition wasobserved in multi-walled nanotubes (catalytically grown orarc-produced), C₆₀, graphite powder or carbon soot collected from theevaporation of graphite electrodes. The present inventors believe thatthe observation of SWNT photo ignition is the first report onphoto-induced burning of any materials caused by a flash of light.

The ignition and burning of SWNTs occur when local increases intemperature are sufficient to initiate the oxidation of the carbon, andpropagate as more heat is released by this exothermic reaction. In orderto understand the necessary conditions for ignition and the damageinflicted on the tubes, samples were subjected to light flashes undervarious environments and analyzed by transmission electron microscopy(TEM). In air, the average light power needed to ignite a SWNT samplewas found to be 100 mW/cm² (±20 mW) for a sample density of about 0.2g/cm³. The rise time of the pulse was 50 μs and the decay time 1.2 ms.When the sample is compacted to higher densities, larger power is neededin order to ignite the SWNT material. For example, for densities greaterthan 1 g/cm³, ignition occurs at about 300 mW/cm². Without wishing to bebound by any particular theory, the present inventors believe that it ismore difficult to ignite the denser samples because of the lack ofoxygen access and loss of heat into the bulk of the denser samples.

The SWNTs form bundles which criss-cross each other in the pristinesample, as shown in FIG. 1A, which is a TEM image of SWNT materialproduced by the arc discharge technique described in Journet, C., Maser,W. K., Bernier, P., Loiseau, A., delaChapelle, M. L., Lefrant, S.,Deniard, P., Lee, R., Fischer, J. E., “Large-scale production ofsingle-walled carbon nanotubes by the electric-arc technique” Nature388, 756-758 (1997). FIG. 1B is an image of remnants of transformed SWNTbundles after they have been exposed to a flash of light.

Without wishing to be bound by any particular theory, the presentinventors believe that the heat pulse generated by the absorption oflight flash will initially be confined to the tubes in a bundle,especially along their axes. Thermal conductivity of nanotubes along thetube axes is expected to be very high as it is along the planes ofgraphite. See Hone, J., Batlogg, B., Benes, Z., Johnson, A. T., Fischer,J. E., “Quantized phonon spectrum of single-wall carbon nanotubes.”Science 289, 1730-1733 (2000), and Berber, S., Kwon, Y. K., Tomanek, D.“Unusually high thermal conductivity of carbon nanotubes.” Phys. Rev.Lett. 84, 4613-4616 (2000). As the material is compacted, such as thedense bucky paper obtained after purification and infiltration ofnanotubes, more and more bundles are in contact with each other, and theheat is rapidly dissipated into the bulk. In other words, the highenergy densities needed for ignition are most easily attained when thebundles are separated, surrounded by oxygen, and the heat wave islocally confined in the nanotube structures.

Since carbon materials, such as nanotubes, oxidize readily at about 700to 800° C., it may be assumed that the samples reached such temperaturesat the light power threshold necessary for ignition. The oxidationtemperature of nanotubes is discussed, for example, in Ajayan, P. M.,Ebbesen, T. W., Ichihashi, T., Iijima, S., Tanigaki, K. & Hiura, H.,“Opening carbon nanotubes with oxygen and implications for filling”Nature 362, 522-525 (1993) and in Tsang, S. C., Harris, P. J. F., Green,M. L. H. “Thinning and opening of carbon nanotubes by oxidation usingcarbon-dioxide” Nature 362, 520-522 (1993). Without wishing to be boundby any particular theory, the present inventors believe that while thismight be at least the average temperature of the sample, locally thetemperature may be much higher in order for the extensive reconstructionto occur. Typically graphitic carbon materials are annealed attemperatures approaching 2800° C. because of the inherent strength ofC═C covalent bond. SWNTs are known to fuse into large tubes attemperatures between 1500 and 2000° C., as discussed in Nikolaev, P.,Thess, A., Rinzler, A. G., Colbert, D. T., Smalley, R. E., “Diameterdoubling of single-wall nanotubes” Chem. Phys. Lett. 266, 422-426 (1997)and Terrones, M., Terrones, H., Banhart, F., Charlier, J. C., Ajayan, P.M. “Coalescence of single-walled carbon nanotubes” Science 288,1226-1229 (2000). For example, on fast annealing of SWNTs at about 1500°C. in helium atmospheres, one of the present inventors observed that thenanotubes underwent morphological and structural transformation intomultiwalled nanotubes and coalesced, larger SWNTs. The reconstructioninto novel structures, such as those seen in FIGS. 3A-D, requires bondbreakage and rearrangements of several carbon atoms. Therefore, theeffective transient temperature within the tubes is probably at least1500° C., while the ambient temperature is maintained below 1500° C.,such as below 700° C., preferably at room temperature of about 25° C.

The effects of a simple camera flash, discussed above, demonstrate howheat confinement in nanostructures can lead to drastic structuraleffects and induce ignition under exposure to conditions where nothingwould have been expected for bulk materials. Nanotubes with singleatomic layer thick walls are representative of such extreme confinementand lend themselves well to photo-induced effect with their black color.

The SWNTs may be used in any suitable device in which optically inducedSWNT transformation is desired. For example, a device contains a deviceshell or housing and a plurality single-walled carbon nanotubes (SWNTs)located in the device shell. The device preferably also is adapted toperform a function when the SWNTs are ignited or reconstructed byexposure to light having a power sufficient to ignite or reconstruct theSWNTs.

The photo induced transformation of SWNTs make SWNTs suitable for usesas remote light induced trigger and ignition devices. For example, atrigger device may comprise a fuse, where SWNTs are placed acrosselectrodes. The light irradiation of the SWNTs transforms the nanotubefuse and breaks the electric path between the electrodes. An outputsection of the trigger device would comprise the electrodes and outputcircuitry. An ignition device may comprise the nanotubes adjacent to anignitable, volatile material or gas generating material, such as thatused in airbags. The flash of light causes the nanotubes to burn, givingoff a spark and igniting the volatile or gas generating material. Thenanotubes may be embedded in a fluid or aerosol containing the volatileor gas generating material. The SWNT transformation could also be usedpossibly to control nanotube reconstruction or linking by adjusting thelight power and wavelength (both in the visible or IR for vibrationalmodes) to select preferentially some tubes over others based on theirelectronic properties. For example, some nanotubes are semiconductingwhile others are metallic. Incident light may couple differently tometallic versus semiconducting nanotubes. Thus, semiconducting ormetallic nanotubes may be selected based on their electronic structureby appropriately selecting the incident light characteristics.

The photo induced transformation of SWNTs may also be used in aprogrammable read only memory (PROM) or an electrically programmableread only memory (EPROM). A prior art PROM, which is also known as fieldprogrammable memory, utilizes an array of fuses connecting a pluralityof conductors or bit lines. The fuses usually comprise a conductivematerial, such as polysilicon strips. Each fuse corresponds to a storagecell. A laser or other intense light is used to selectively destroy orblow some but not other fuses in the array. In other words, the laser isused to melt the polysilicon strips to disconnect the bit lines at somestorage cell locations but not at other locations to form thenon-volatile memory device. A blown storage cell corresponds to a “0”data bit, while an intact storage cell corresponds to a “1” data bit. Byselectively blowing some storage cells, a pattern of 1 and 0 data bitsis stored in the PROM. The data is later read out by applying a readvoltage to the bit lines and detecting a current flow between the bitlines.

A prior art EPROM usually utilizes an array of floating gatetransistors. The EPROM is electrically programmed by applying a voltagebetween a source and a drain or between a source and a control gate of aparticular transistor to inject electrons into the floating gate. Thestored electron charge in the floating gate alters the threshold voltageof a particular transistor, changing its memory state from “0” to “1”.The transistors of the EPROM are erased by masking certain transistorsand leaving other transistors unmasked, and exposing the EPROM to UV.The UV removes the charge stored in the floating gates of the unmaskedtransistors, changing their memory state from “1” to “0”. The programmedmasked transistors retain the “1” memory state.

In a preferred aspect of the present invention, SWNTs may be used toreplace fuses and floating gate transistors in a PROM and an EPROM,respectively. For example, in a PROM, at least one SWNT, such as anarray of SWNT bundles, is used to connect a plurality of conductors orbit lines. In one preferred, non-limiting embodiment shown in FIG. 4,the PROM 10 may be arranged in a classic cross bar architecture. In thisarchitecture, intersecting bit lines 12 and 14 arranged at about 90degree angles and connected at storage cell locations by SWNT bundles16A, 16B. The vertical bit lines 12 are not otherwise electricallyconnected to the horizontal bit lines 14. The unprogrammed PROM arrayhas “1” stored in each storage cell location because the SWNT bundlesprovide an electrical connection between adjacent bit lines 12, 14.

To program the PROM 10, light (i.e., visible, UV or IR) is selectivelyapplied to some but not other storage cell locations to selectivelytransform (i.e., ignite or reconstruct) some SWNT bundles but not othersSWNT bundles. For example, light, such as a flash of white light, may beused to transform SWNT bundle 16A but not bundle 16B. The light may beselectively applied to different SWNT bundles by focusing the light tothe dimension of one bundle. The focused light may be scanned across thePROM array 10 and selectively turned on only over selected SWNT bundlelocations. Alternatively, the light may be selectively applied byselectively masking some but not other SWNT bundles. For example, aphotoresist mask may be formed over selected SWNT bundles.Alternatively, a solid, opaque mask, such as a metal, glass or plasticmask, with transparent portions or windows, may be interposed betweenthe light source and the PROM 10. The entire PROM 10 or part of the PROM10 is then irradiated with the light to transform the unmasked SWNTbundles. The step of exposing the SWNT to light having a powersufficient to ignite or reconstruct the SWNT causes the SWNTs todisconnect the bit lines. The transformed SWNT bundles are convertedfrom a “1” to a “0” memory state because the transformed SWNT bundles nolonger provide an electrical contact between adjacent bit lines 12, 14.The PROM also contains an output section which comprises a peripheralcircuit adapted to output a read signal, similar to a peripheral ordriver circuit used in semiconductor PROMs. The peripheral circuit maycomprise a CMOS logic circuit for example.

The array 10 may also be made as an EPROM. In this case, the SWNTbundles 16A, 16B may be made to shift to contact or not contact adjacentbit lines 12, 14 by passing a current through the bit lines. The currentcauses the SWNTs to shift, creating and open or closed circuit. TheEPROM is erased by selectively exposing the SWNT bundles 16A or 16B tolight to transform the irradiated bundles. The EPROM also contains anoutput section which comprises a peripheral circuit adapted to output aread signal, similar to a peripheral or driver circuit used insemiconductor EPROMs.

SPECIFIC EXAMPLES

The ignition and burning of SWNTs exposed to a photo flash of whitelight are shown in FIGS. 2A-E. FIGS. 2A-E depict a sequence of fourframes taken from a real-time video recording of burning SWNTs made bythe HiPCo process after the application of the photo flash. The SWNTswere located in an air ambient at room temperature. FIG. 2A illustratesthe original SWNT sample showing the flash on top of about 2 cm outsidediameter. Immediately after the flash, several red spots were observedon the sample. FIGS. 2B and 2C show the sample soon after flashingexhibiting the ignited SWNT material with red and yellow spots. FIG. 2Dshows the sample during burning depicting only red spots (i.e., thered-hot regions within the sample). As the sample then burns down inair, it generates CO and CO₂, and leaves behind residues comprisingoxidized catalyst particles, such as Ni—Y or Fe, utilized for SWNTsynthesis (a red powder) as well as carbonaceous materials (a blackmaterial), which are shown in FIG. 2E. Without wishing to be bound by aparticular theory, the present inventors believe that it is highlypossible that although conduction along the tube axis is high, thecontacts (bad thermal contacts) between bundles and individual nanotubescould act as “hot” spots, resulting in the formation of hot localizedheating centers and acting as ignition triggers in the presence of air.

Thus, the present inventors were able to obtain light emission from ananotube, such as nanotubes located in a bundle, by exposing thenanotube to first light, such as the photo flash of white light, suchthat the nanotube emits second light, such as red and yellow light, dueto the exposure to the first light. The first light, such as whitelight, and the second light, such as yellow and red light, compriselight of a different peak wavelength. The second light, such as the redand yellow light was recorded, such as with a video or a still camera.

However, the present invention should not be considered limited by thepreferred embodiment described above. For example, the term light mayinclude infrared or ultraviolet radiation in addition to visible light.For example, isolated nanotubes exhibit fluorescence in the infraredrange when they are irradiated with visible light from a laser, asdiscussed in M. J. O'Connell, et al., 297 Science 593 (Jul. 26, 2002),incorporated herein by reference in its entirely. As described in theO'Connell et al. article, single walled, semiconducting nanotubesencapsulated in cylindrical SDS micelles exhibited fluorescence in the1500 to 875 nm range after being irradiated with a pulsed 532 nm laser.Thus, nanotube bundles and single nanotubes may be used to emit light.

The reconstruction of SWNTs exposed to a photo flash in differentambients is illustrated in FIGS. 3A-D. FIGS. 3A-D are high resolutiontransmission electron microscopy (HRTEM) images of a typical areas ofcarbonaceous material obtained after flashing SWNTs in differentambients. These Figures reveal that, independent of ignition, thematerial undergoes surprisingly large structural reconstruction.

The SWNT samples before flashing contained a large amount of SWNTbundles with well defined cross sections. The samples also contain a lowyield of carbon nanohorns. Nanohorns are described, for example, inIijima, S., Yudasaka, M., Yamada, R., Bandow, S., Suenaga, K., Kokai,F., Takahashi, K., “Nano-aggregates of single-walled graphitic carbonnano-horns.” Chem. Phys. Lett. 309, 165-170 (1999), incorporated hereinby reference. FIG. 3A is a HRTEM image of reconstructed SWNTs that wereexposed to a photographic flash in an air ambient at atmosphericpressure and room temperature. In the sample that was exposed to theflash in air, in the absence or presence of ignition, much of theremaining carbon material was transformed into single layered or singlewalled structures with many conical tips similar to nanohorns. Inaddition to the nanohorns, some SWNT bundles surrounded by amorphouscarbon were observed. Thus, the SWNTs were heavily damaged and metallicparticles were embedded in amorphous-like carbon domains, possibly dueto the fragmentation of the nanotubes. While a few undamaged SWNTs wereobserved, no cross sections were observed.

FIG. 3B is a HRTEM image of reconstructed SWNT bundles that were exposedto a photographic flash in an argon ambient. FIG. 3B shows that afterthe flashing and reconstruction, filamentous structures that arecomposed of SWNTs in their cores covered by reconstructed curledgraphene (amorphous-like) material remain. Thus, the reconstructedsample contained SWNT bundles coated with amorphous carbon as well asareas containing nanohorns and a few “graphitic” domains. The coatedbundles appeared crystalline on the inside but were damaged on theoutside. However, the SWNTs were not as heavily damaged as in the caseof helium ambient described below. The bundle cross sections were easyto find. The present inventors also observed agglomerates of nanohornsaround the SWNTs, but at a much lower yield than compared to SWNTbundles reconstructed in a helium ambient under the same conditions, asdescribed below.

FIG. 3C is a HRTEM image of reconstructed SWNT bundles that were exposedto a photographic flash under a vacuum of about 1×10⁻⁴ Torr. The imageshows that the nanotube bundles were totally damaged and no innernanotube cores were observed. Some graphitic domains, nanohorns andtraces of SWNTs were also observed. The experiment was repeated but withfive flashes instead of one. The sample was also heavily damaged, and alarge number of graphitic domains were present (e.g. 3-8 graphiticlayers stacked in random orientations). Some nanohorns and metalparticles embedded in amorphous-like carbon material were also observed.SWNTs were only observed in one location, and were severely damaged andexhibited large quantities of amorphous material around the bundles.Thus, the additional flashes resulted in a more several transformationor damage. Furthermore, the additional flashes resulted in additionalgraphitic domains compared to one flash. This indicates that the SWNTsexposed to five flashes suffered severe reconstruction into flatdomains, which tend to be energetically more favorable than curvedsurfaces.

FIG. 3D is a HRTEM image of reconstructed SWNT bundles that were exposedto a photographic flash in a helium ambient. The image shows that thestructure exhibits complete destruction of the tubes and formation of alarge amount of nanohorns and some graphitic domains (e.g. 3-4 stackedlayers in random orientations). More nanohorns but less SWNTs wereobserved than in the case of the flash under vacuum. The observed SWNTshave been shortened and it was easier to find their tips, which appearto be heavily damaged than in the unflashed SWNT samples. This may beuseful for applications where it is important to shorten SWNTs and/or tofind SWNT tips.

The SWNT bundles appear to remain at first glance after being flashedunder vacuum or in an argon ambient. However, upon closer inspection,the bundles are heavily damaged with significant reconstruction and theappearance of filamentous, partially graphitized and disordered carbon,as shown in FIGS. 3B and 3C. In contrast, the samples in which SWNTbundles that were flashed in a helium ambient exhibit very few nanotubesbundles and large amounts of nanohorn material, as shown in FIG. 3D.Thus, it is possible to form carbon nanohorns by exposing SWNTs tolight. Furthermore, the SWNT samples were transformed or damaged by theflash in light on all four ambients.

Without wishing to be bound by a particular theory, the presentinventors believe that the difference in reconstructed material may bedue to the difference in thermal conductivity of the ambient. Vacuum andargon ambient have a low thermal conductivity compared to heliumambient. For example, argon has a thermal conductivity of 0.0177 Wm⁻¹K⁻¹ while helium has a thermal conductivity of 0.152 Wm⁻¹ K⁻¹. Thepresent inventors believe that much more amorphous material is observedaround very damaged nanotubes in argon and vacuum than in helium. Inother words more deconstruction than reconstruction takes place in a lowthermal conductivity ambient, such as vacuum or argon. In vacuum,several flat graphitic-like domains (3-8 randomly stacked graphiticstructures) are also found. In air, a reaction between carbon and oxygenshould occur. In this case, the reconstruction takes place but theinfluence of oxygen may also be important.

Generally, samples treated in the absence of oxygen experience severereconstruction of the SWNTs, which fragment and reconstruct intometastable carbon nanostructures. These structures are notthermodynamically stable any more than nanotubes. The carbon atoms wouldtend to form planar graphitic stacks, which appear to be more stablethan bent domains. Therefore, as the heat rises in the nanotubes,reconstruction begins and continues as long as the heat is notdissipated. If the heat dissipates fast, such as in a high thermalconductivity ambients, such as helium, the resulting structures aresnapshots at different stages of reconstruction. In Ar or in vacuum,where the heat is not carried away so easily, the material continues todeconstruct, reforming into thermodynamically favored single layeredgraphitic domains. In fact, the structural reconstructions in samplesflashed with several consecutive shots leads to the formation of largerstacked “graphitic” domains of 4-10 layers. A higher thermalconductivity of the ambient gas also provides a mechanism for heatspreading through the sample, leading to more uniform structural damage.Another factor that may influence SWNT transformation is the SWNTthermal conductivity, which is relatively high. The contacts of the SWNTbundles may also be a factor in the burning of the SWNT samples. Thesamples reconstruct and SWNTs transform into a graphene arrangementafter flashing, while the presence of air and helium ambient and the waythe SWNTs are entangled enhances the effect.

The SWNT samples used in the specific examples include: (a) as grownSWNTs produced using the arc discharge (in 500 Torr He atmospheres)between graphite electrodes loaded with Ni—Y mixtures, see Journet, C.,Maser, W. K., Bernier, P., Loiseau, A., delaChapelle, M. L., Lefrant,S., Deniard, P., Lee, R., Fischer, J. E., “Large-scale production ofsingle-walled carbon nanotubes by the electric-arc technique” Nature388, 756-758 (1997); (b) commercially available SWNTs produced by theHiPCo process, see Nikolaev, P., Bronikowski, M. J., Bradley, R. K.,Robmund, F., Colbert, D. T., Smith, A., Smalley, R. E., “Gas-phasecatalytic growth of single-walled carbon nanotubes from carbon monoxide”Chem. Phys. Lett. 313, 91-97 (1999); c) as grown SWNTs produced by laserablation of graphite-Ni—Co mixtures in Ar at 1500° C., see Thess, A.,Lee, R., Nikolaev, P., Dai, H. J., Petit, P., Robert, J., Xu, C. H.,Lee, Y. H., Kim, S. G., Rinzler, A. G., Colbert, D. T., Scuseria, G. E.,Tomanek, D., Fischer, J. E., Smalley, R. E. “Crystalline ropes ofmetallic carbon nanotubes” Science 273, 483-487 (1996), and (d) Buckypaper purchased from CARBOLEX Inc. (www.carbolex.com). For themicroscopy studies of the light-flash experiments in differentatmospheres, SWNTs were deposited on TEM copper and silver grids, whichwere inserted inside optical cells, evacuated, and subsequently purgedwith ultrahigh purity He or Ar gas (atmospheric pressure). For vacuumsamples, the pressure was maintained at 1×10⁻⁴ Torr. High resolutiontransmission electron microscopy (HRTEM) studies were carried out in aJEOL JEM-4000 microscope operating at 400 kV and a JEOL JEM 2010operated at 200 kV and equipped with EDX detector and a Gatan multiscancamera.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents. All articles mentioned herein are incorporated by referencein their entirety.

1. A method of obtaining light emission from a nanotube, comprisingexposing the nanotube to a first light such that the nanotube emits asecond light due to the exposure to the first light.
 2. The method ofclaim 1, wherein the first light and the second light comprise light ofa different peak wavelength.
 3. The method of claim 1, wherein the firstlight comprises white light and the second light comprises red or yellowlight.
 4. The method of claim 1, further comprising recording the secondlight.
 5. A method of obtaining light emission from a nanotube,comprising exposing the nanotube to a first stimulus such that thenanotube emits light due to the exposure to the first stimulus.
 6. Aluminescent light source comprising semiconducting single-wall carbonnanotubes.
 7. The light source of claim 6, wherein the light is in thenear-infrared region of the electromagnetic spectrum.